The present invention generally relates to components for catheters having inflation devices or balloons for percutaneous transluminal angioplasty, and more particularly to a syringe assembly for inflating and for rapidly deflating an angioplasty balloon component of a catheter to which the inflation syringe assembly is attached.
Great strides have been made in combating blood vessel diseases such as atherosclerosis, which is the increasing deposit of fatty and fibrous plaque that ultimately blocks arteries and other blood vessels. A number of surgical and non-surgical treatments are in use or are proposed. Bypass surgery has been practiced extensively but because of the expense and risks involve,, non-surgical treatments have as of late received particular attention.
Balloon angioplasty, one such non-surgical technique which may be considered to be gaining in popularity, is technically referred to as a percutaneous transluminal angioplasty procedure in which a cardiologist performs the procedure with the patient under local anesthesia. A catheter with a dilatable balloon at or near its tip is threaded into and through an artery and to the stenotic region. The balloon is then inflated thereby compressing the plaque against and into the arterial wall. In this manner the vessel's interior diameter is widened to again permit sufficient flow of blood. This procedure is utilized in the peripheral arteries as well as the coronary arteries.
Typically, the balloon is inflated utilizing a fluid such as a mixture of equal parts of a contrast media and saline solution, which fluid exerts the dilatation pressure. An inflation syringe assembly or device is utilized to deliver the inflation media or fluid to the balloon as well as to provide the pressure needed for dilatation. Continuous pressure readings can be developed by having the inflation syringe assembly coupled in series to a pressure reading device uuch as a manometer.
It is important that the inflation syringe assembly not only deliver fluid and maintain the pressure but also, in particular, release the pressure rapidly when needed. Various designs of syringe assemblies have been utilized and found capable of delivering fluid to a predetermined pressure, but many such devices have been found to be unsatisfactory. Some such devices do not adequately maintain a predetermined pressure for a sufficient period of time as might be required by the physician, such devices tending to "leak" due to inadequate positive pressure control, which adds a further and troublesome complexity to the procedures. In order to obtain the requisite mechanical advantage in positively and incrementally inflating the balloon to higher pressures such as on the order of 450 psi and above, the typical structure provided achieves threaded advancement and usually includes a syringe piston that is advanced by a screw threaded rod engaged with a longitudinally fixed mating threaded member.
This type of positive threaded action usually provides the requisite incremental pressurization of the balloon under controlled conditions, but retraction of the piston at the same slow rate as is needed during advancement is not acceptable in the event that emergency depressurization or the like is necessary. In the event of an emergency or in order to conduct these types of procedures in a manner that avoids unnecessary delays, the balloon must be capable of being deflated as quickly as possible. For purposes of rapid dellation, syringe devices of this type have been constructed with manually movable threadedly mating members which can be disengaged from a threaded rod in an effort to achieve rapid retraction of the threaded rod and its attached syringe piston.
Utilizing the foregoing design approach, certain difficulties have been encountered. For example, it has been found to be extremely difficult to prevent a movable or pivotable threadedly engageable member from being a source of pressure leakage because of a tendency of such member to ride on top of the mating threads of the rod. Thus, proposed designs include the foregoing disadvantage in that the movable or pivotable threadedly engageable member is not sufficiently positively acting and directly responsive through its movement between engaged and disengaged positions. Still further, the rapidity with which the movable threadedly engageable member is completely withdrawn from threaded engagement with the piston rod can be unsatisfactory. While complete disengagement in a time period of on the order of less than one half of a second is extremely important, known devices take at least one second or longer at higher pressures. Furthermore, known devices lack sufficient leverage for rapid disengagement of the threadedly engageable member thus making it extremely difficult, and sometimes impossible, to obtain complete disengagement at pressures of from about 100 to about 150 psi and above.
The inflation syringe assembly of the present invention overcomes these types of shortcomings. By reason of positive engagement between an improved movable partially threaded member and the threaded piston rod, back pressure leakage is eliminated. The movable partially threaded engagement member is structured in such a manner that it rapidly and completely disengages its threaded portion from the piston rod in order to effect almost instantaneous balloon depressurization action by reason of the degree to which it is engageable and disengageable with the rod, as well as due to the direction of its travel to effect engagement and disengagement. Still further, a manually operated lever provides for mechanically advantageous establishment of rapid and positive disengagement that achieves positive and quick disengagement action.